Monoclonal antibodies that bind to SSEA4 and uses thereof

ABSTRACT

An isolated monoclonal antibody or antigen-binding fragment that specifically binds to stage-specific embryonic antigen 4. The monoclonal antibody or antigen-binding fragment includes a heavy-chain CDR1 having the sequence of SEQ ID NO: 33 or SEQ ID NO: 40, a heavy-chain CDR2 having the sequence of SEQ ID NO: 34 or SEQ ID NO: 39, a heavy-chain CDR3 having the sequence of SEQ ID NO: 35 or SEQ ID NO: 41, a light-chain CDR1 having the sequence of SEQ ID NO: 36 or SEQ ID NO: 42, a light-chain CDR2 having the sequence of SEQ ID NO: 37 or SEQ ID NO: 43, and a light-chain CDR3 having the sequence of SEQ ID NO: 38 or SEQ ID NO: 44. Also disclosed is an anti-tumor method carried out by administering the above monoclonal antibody or antigen-binding fragment to a subject having a tumor that expresses stage-specific embryonic antigen 4. Further provided are nucleic acids encoding the above sequences and recombinant cells containing the nucleic acids.

BACKGROUND

The goal of immunotherapy for cancer is to increase the strength of a patient's own immune responses against tumors. Immunotherapy can stimulate the activities of specific components of the immune system against cancer cells or can counteract signals produced by the cancer cells that suppress immune responses.

For example, antibodies have been developed as cancer vaccines which bind specifically to tumor-associated antigens (TAAs), e.g., protein antigens and carbohydrate antigens, on the surface of cancer cells, leading to antibody-dependent cellular cytotoxicity, antibody-dependent phagocytosis, and complement-dependent cell lysis, as well as direct cytostatic and/or cytotoxic effects.

Monoclonal antibody-based anti-cancer vaccines against several carbohydrate TAAs, e.g., Globo H, stage-specific embryonic antigen 3, and stage-specific embryonic antigen 4, have been developed. Yet, the need exists for improved monoclonal antibodies as anti-cancer vaccines having higher affinity for the carbohydrate TAA in order to promote more effective killing of cancer cells and to provide long-lasting resistance to cancer relapse.

SUMMARY

To meet the need set forth above, an isolated monoclonal antibody or antigen-binding fragment thereof is provided that specifically binds to stage-specific embryonic antigen 4 (SSEA4). The monoclonal antibody or antigen-binding fragment includes a heavy-chain CDR1 having the sequence of SEQ ID NO: 33 or SEQ ID NO: 40, a heavy-chain CDR2 having the sequence of SEQ ID NO: 34 or SEQ ID NO: 39, a heavy-chain CDR3 having the sequence of SEQ ID NO: 35 or SEQ ID NO: 41, a light-chain CDR1 having the sequence of SEQ ID NO: 36 or SEQ ID NO: 42, a light-chain CDR2 having the sequence of SEQ ID NO: 37 or SEQ ID NO: 43, and a light-chain CDR3 having the sequence of SEQ ID NO: 38 or SEQ ID NO: 44.

An isolated monoclonal antibody falling within the scope of the invention includes a heavy-chain sequence selected from SEQ ID NO: 2, SEQ ID NO:6, SEQ ID NO: 10, SEQ ID NO: 12, SEQ ID NO: 14, SEQ ID NO: 22, SEQ ID NO: 24, and SEQ ID NO: 26; and a light-chain sequence selected from SEQ ID NO: 4, SEQ ID NO: 8, SEQ ID NO: 16, SEQ ID NO: 18, SEQ ID NO: 20, SEQ ID NO: 28, SEQ ID NO: 30, and SEQ ID NO: 32.

Also provided is a method for treating a tumor in which cells in the tumor express SSEA4. The method is accomplished by administering an effective amount of the monoclonal antibody or antigen-binding fragment described above.

Further disclosed is a nucleic acid construct that encodes the above-described monoclonal antibody or antigen-binding fragment thereof, as well as a recombinant cell containing the nucleic acid construct. The recombinant cell expresses a monoclonal antibody or antigen-binding fragment thereof that specifically binds to SSEA4.

The details of several embodiments of the present invention are set forth in both the description and the drawings below. Other features, objects, and advantages of the invention will be apparent from the description and also from the appended claims. Finally, all references cited herein are hereby incorporated by reference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

The description below refers to the accompanying drawings, of which:

FIG. 1A is an amino acid alignment of germline human IGHV4-59x01 heavy-chain variable region (huIGHV4-59x01: SEQ ID NO: 60) and corresponding amino acid sequences of anti-SSEA4 murine monoclonal antibody 1 (muMAb1 H; residues 20-138 of SEQ ID NO: 2) and human monoclonal antibody 1 sequences (huMAb1 H, residues 20-138 of SEQ ID NO: 10; huMAb1 H1, residues 20-138 of SEQ ID NO: 12; huMAb1 H2, residues 20-138 of SEQ ID NO: 14), the CDR regions being enclosed in boxes in this figure and all the other figures;

FIG. 1B is an amino acid alignment of germline human IGKV3-11x01 light-chain variable region (huIGKV3-11x01; SEQ ID NO: 61) and corresponding amino acid sequences of anti-SSEA4 murine monoclonal antibody 1 (muMAb1 L; residues 23-128 of SEQ ID NO: 4) and human monoclonal antibody 1 sequences (huMAb1 L, residues 23-128 of SEQ ID NO: 16; huMAb1 L1, residues 23-128 of SEQ ID NO: 18; huMAb1 L2, residues 23-128 of SEQ ID NO: 20);

FIG. 2A is an amino acid alignment of germline human IGHV4-59x01 heavy-chain variable region (huIGHV4-59x01: SEQ ID NO: 60) and corresponding amino acid sequences of anti-SSEA4 murine monoclonal antibody 2 (muMAb2 H; residues 20-139 of SEQ ID NO: 6) and human monoclonal antibody 2 sequences (huMAb2 H, residues 20-139 of SEQ ID NO: 22; huMAb2 H1, residues 20-139 of SEQ ID NO: 24; huMAb2 H2, residues 20-139 of SEQ ID NO: 26); and

FIG. 2B is an amino acid alignment of germline human IGKV3-11x01 light-chain variable region and corresponding amino acid sequences of anti-SSEA4 murine monoclonal antibody 2 (muMAb2 L; residues 23-128 of SEQ ID NO: 8) and human monoclonal antibody 2 sequences (huMAb2 L, residues 23-128 of SEQ ID NO: 28; huMAb2 L1, residues 23-128 of SEQ ID NO: 30; huMAb2 L2, residues 23-128 of SEQ ID NO: 32).

DETAILED DESCRIPTION

As set forth, supra, a monoclonal antibody or antigen-binding fragment, e.g., single chain Fv, having the indicated CDR regions is provided that specifically binds to stage-specific embryonic antigen 4 (SSEA4). In an exemplary monoclonal antibody or antigen-binding fragment, the heavy-chain CDR1 (H-CDR1) has the sequence of SEQ ID NO: 33, the heavy-chain CDR2 (H-CDR2) has the sequence of SEQ ID NO: 34, the heavy-chain CDR3 (H-CDR3) has the sequence of SEQ ID NO: 35, the light-chain CDR1 (L-CDR1) has the sequence of SEQ ID NO: 42, the light-chain CDR2 (L-CDR2) has the sequence of SEQ ID NO: 43, and the light-chain CDR3 (L-CDR3) has the sequence of SEQ ID NO: 44.

Examples of monoclonal antibodies having the CDR regions identified in the preceding paragraph have the following combinations of heavy-chain sequence and light-chain sequence: (i) the heavy-chain sequence of SEQ ID NO: 14 and the light-chain sequence of SEQ ID NO: 28, (ii) the heavy-chain sequence of SEQ ID NO: 14 and the light-chain sequence of SEQ ID NO: 30, (iii) the heavy-chain sequence of SEQ ID NO: 14 and the light-chain sequence of SEQ ID NO: 32, (iv) the heavy-chain sequence of SEQ ID NO: 2 and the light-chain sequence of SEQ ID NO: 4, and (v) the heavy-chain sequence of SEQ ID NO: 6 and the light-chain sequence of SEQ ID NO: 8.

A nucleic acid construct encoding the monoclonal antibody or binding fragment includes sequences that encode the H-CDR1, H-CDR2, H-CDR3, L-CDR1, L-CDR2, and L-CDR3 regions listed above. In an example, the nucleic acid construct encodes the amino acids of SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 42, SEQ ID NO: 43, and SEQ ID NO: 44.

In another aspect, the nucleic acid construct encodes a monoclonal antibody having the combinations of heavy-chain and light-chain sequences delineated above. Specific examples of such a nucleic acid construct each include one of the following combinations of sequences: (i) SEQ ID NO: 13 and SEQ ID NO: 27, (ii) SEQ ID NO: 13 and SEQ ID NO: 29, (iii) SEQ ID NO: 13 and SEQ ID NO: 31, (iv) SEQ ID NO: 1 and SEQ ID NO: 3, and (v) SEQ ID NO: 5 and SEQ ID NO: 7.

Moreover, a recombinant cell is provided that contains any of the just-mentioned nucleic acid constructs and expresses a monoclonal antibody or a binding fragment that specifically binds to SSEA4. A particular recombinant cell expresses a monoclonal antibody or binding fragment having the following CDR sequences: SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 42, SEQ ID NO: 43, and SEQ ID NO: 44. An example of such a recombinant cell expresses a monoclonal antibody having the heavy-chain sequence of SEQ ID NO: 14 and the light-chain sequence of SEQ ID NO: 28.

The method mentioned above for treating a tumor can be carried out by administering any of the monoclonal antibodies disclosed in the application. In one example, the monoclonal antibody includes SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 42, SEQ ID NO: 43, and SEQ ID NO: 44. The monoclonal antibody can have the heavy-chain sequence of SEQ ID NO: 14 and the light-chain sequence of SEQ ID NO: 28.

The tumor-treating method can be effective for treating breast, colon, gastrointestinal, kidney, lung, liver, ovarian, pancreatic, rectal, stomach, testicular, thymic, cervical, prostate, bladder, skin, nasopharyngeal, esophageal, oral, head and neck, bone, cartilage, muscle, lymph node, bone marrow, and brain cancer.

Without further elaboration, it is believed that one skilled in the art can, based on the disclosure herein, utilize the present disclosure to its fullest extent. The following specific examples are, therefore, to be construed as merely descriptive, and not limitative of the remainder of the disclosure in any way whatsoever. All publications and patent documents cited herein are incorporated by reference in their entirety.

EXAMPLES Example 1: Hybridoma Production

Murine monoclonal antibodies against SSEA4 were produced using standard procedures. Briefly, mice were injected with SSEA4 fused to bovine serum albumin (BSA-SSEA4) together with an adjuvant once every two weeks for up to 10 weeks. Anti-SSEA4 antibody titers in blood samples were assayed by enzyme-linked immunosorbent assay (ELISA) using ELISA plates with bound BSA-SSEA4 under standard conditions.

Blood samples from mice having the highest titer by BSA-SSEA4 ELISA were also tested by ELISA using human pancreatic cancer (HPAC) cells that express SSEA4.

Splenocytes were isolated from the two mice having the highest antibody titers and fused with myeloma cells to form hybridomas using standard techniques. Hybridomas producing high titers of anti-SSEA4 antibodies were identified using standard subcloning procedures and ELISA assays with BSA-SSEA4 and HPAC cells. Hybridomas producing antibodies that bound to both HPAC and human melanoma cell line A375, which does not express SSEA4, were not pursued further.

Antibodies binding to cell surface SSEA4 were validated using a fluorescence-activated cell sorting assay by incubating HPAC cells and A375 cells with hybridoma supernatants, followed by incubation with a fluorescently labelled secondary antibody. Two monoclonal antibodies, designated as murine monoclonal antibody 1 (muMAb1) and murine monoclonal antibody 2 (muMAb2), were selected for further analysis. Both of these monoclonal antibodies bind to BSA-SSEA4 and HPAC cells and do not bind to A375 cells.

Isotype analysis indicated that muMAb1 is an IgG1 kappa antibody and muMAb2 is an IgG3 kappa antibody.

Monoclonal antibody concentrations in hybridoma supernatants and binding affinity for SSEA4 were determined as described in the following two sections. The K_(d) value for muMAb1 was 0.22 nM and the K_(d) value for muMAb2 was 0.08 nM.

Example 2: Determination of Antibody Concentration by ELISA

The concentrations of muMAb antibodies in media samples were determined by ELISA with the following primary antibodies coated on ELISA plates. For murine MAbs, ELISA plates were coated with AffiniPure Goat Anti-Mouse IgG (H+L) (Jackson ImmunoResearch #115-005-062) at 1 μg/ml, 100 μl/well overnight. After incubation with serial dilution of hybridoma supernatants or media samples from transient transfections (see below), wells were washed thoroughly and bound antibodies detected by adding Peroxidase AffiniPure Goat Anti-Mouse IgG (H+L) (Jackson ImmunoResearch #115-035-062) at a 1:8,000 dilution. After thorough washing, ABTS Peroxidase Substrate (1 Component) (KPL #50-66-06) was added and absorbance of each well at 405 nm was measured.

For humanized mAbs (see below), ELISA plates were coated with AffiniPure F(ab′)₂ Fragment Goat Anti-Human IgG, Fcγ Fragment Specific (Jackson ImmunoResearch #109-006-098) 1 μg/ml, 100 μl/well, overnight. Detection of bound humanized antibodies was performed using Peroxidase AffiniPure Goat Anti-Human IgG, Fcγ fragment specific (Jackson ImmunoResearch #109-035-008) at a 1:10,000 dilution as described above for murine antibodies.

Example 3: Determination of Antibody Affinities by ELISA

Standard ELISA procedures were performed for the determination of antigen binding affinity using the following sets of reagents. ELISA plates were coated with BSA-SSEA4 at a 1:1000 dilution. Samples of serially-diluted hybridoma supernatants or transient transfection samples were added to each well, followed by thorough washing. The following secondary antibodies were used to detect muMAbs and huMAbs bound to the antigen on the plate: For muMAb1, AffiniPure Goat Anti-Mouse IgG, Fcγ Subclass 1 Specific (Jackson ImmunoResearch #115-005-205) at a 1:2,500 dilution, for muMAb2, AffiniPure Goat Anti-Mouse IgG, Fcγ Subclass 3 Specific (Jackson ImmunoResearch #115-005-209) at a 1:2,500 dilution, for all humanized antibodies, AffiniPure Goat Anti-Human IgG (H+L) (Jackson ImmunoResearch #109-005-088) at a 1:2,500 dilution.

Plate-bound secondary antibodies were detected using Peroxidase AffiniPure Bovine Anti-Goat IgG (H+L) (Jackson ImmunoResearch #805-035-180) at a 1:6,000 dilution and developed as set forth above.

Example 4: Cloning of Antibody Genes

VH and VL antibody sequences were cloned from hybridomas as follows. Total RNA was isolated from approximately 5-7×10⁶ hybridoma cells using TRIZOL reagent (Invitrogen, cat #15596-026) as directed by the manufacturer. First strand cDNA synthesis was carried out using Maxima Universal First Strand cDNA synthesis kit (Thermo Fisher cat. # K1661) with 6 μg total RNA and the following gene specific primers: murine IgG1 VH: TATGCAAGGCTTACAACCACA (SEQ ID NO: 45), murine IgG3 VH: GGGGGTACTGGGCTTGGGTAT (SEQ ID NO: 46), and murine kappa VL: CTCATTCCTGTTGAAGCTCTTGAC (SEQ ID NO: 47).

Following first strand cDNA synthesis, a poly A sequence was appended to the 5′ end of each first strand cDNA with terminal transferase. The resultant 5′ end tailed cDNA products were subjected to two rounds of PCR amplification. The first round PCR reaction was carried out with Herculase II DNA polymerase (Agilent Technologies cat #600679) with the following primers: 5′ GTGACTCGAGTCGACATCGA TTTTTTTTTTTTTTTTT (SEQ ID NO: 48), 3′ primer for murine IgG1 VH: CTTCCGGAATTCCTCAATTTTCTTGTCCACCTTGGTGC (SEQ ID NO: 49), 3′ primer for murine IgG3 VH: CTTCCGGAATTCCTCGATTCTCTTGATCA ACTCAGTCT (SEQ ID NO: 50), and 3′ primer for murine kappa VL: CTTCCGGAATTCCTCATTCCTGTTGAAGCTCTTGACAATGGG (SEQ ID NO: 51).

A fraction ( 1/20) of the first round PCR products was further amplified in a second round of PCR using Phusion High Fidelity DNA polymerase (Fisher Scientific cat # F530L) with the following primers: 5′ GTGACTCGAGTCGACATCGATTT TTTTTTTTTTTTTT (SEQ ID NO: 48), 3′ primer for murine IgG1 VH: ATTAAGTCGACATAGACAGATGGGGGTGTCGTTTTGGC (SEQ ID NO: 52), 3′ primer for murine IgG3 VH: ATTAAGTCGACAGGGACCAAGGGATAG ACAGATGG (SEQ ID NO: 53), and 3′ primer for murine kappa VL: CTACCTCGAGGGATACAGTTGGTGCAGCATC (SEQ ID NO: 54).

The resulting PCR products were digested with pairs of restriction enzymes, ClaI/S all for the VH PCR fragments and ClaI/XhoI for the VL PCR fragments and inserted into a cloning vector using standard recombinant DNA procedures. Clones containing inserts in the appropriate size range were sequenced in order to identify full length VH/VL clones.

Example 5: Construction of Full-Length Murine Antibody Expression Vectors

Full-length murine IgG heavy and light chain expression plasmids were constructed as follows.

First strand cDNA synthesis was carried out by reverse transcriptase (RT) using Maxima Universal First Strand cDNA synthesis kit (Thermo Fisher cat # K1661) with 6 μg total RNA from hybridomas identified above as containing full-length VH and VL sequences. An oligo dT primer and random hexamer primers were employed in separate RT reactions. The oligo dT and random primed RT products were combined and used as the source of full length cDNA for muMAb1 and muMAb2, via a round of PCR amplification using Phusion High Fidelity DNA polymerase (Fisher Scientific cat # F530L) with the following set of primers, which were designed using the sequence information obtained above. For muMAb1 and muMAb2 kappa light chain 5′ primer CAGTCCGCGGCCACCATGGATTTTCAAGTGCAGATTTTC (SEQ ID NO: 55), 3′ primer AGGAAGATCTAACACTCATTCCTGTTGAAGC (SEQ ID NO: 56). For muMAb1 murine IgG1 heavy chain 5′ CAGTCCGCGGCCACCATGGCTGTC CTGGTGCTGTT (SEQ ID NO: 57), 3′ primer CTGGACAGGGATCCAGAGTTCCA (SEQ ID NO: 58). For muMAb2 murine IgG3 heavy chain 5′ primer CAGTCCGCGG CCACCATGGCTGTCCTGGTGCTGTT (SEQ ID NO: 57), 3′ primer CATGAGA TCTCATTTACCAGGGGAGCGAGA (SEQ ID NO: 59).

The amplified muMAb1 and muMAb2 murine kappa light chain sequences and the muMAb2 murine IgG3 heavy chain sequence were directly cloned into a mammalian expression plasmid as SacII/BglII restriction fragments. The muMAb1 murine IgG1 heavy chain amplification product represents the 5′ end of the gene coding sequences, just past an internal BamHI site that corresponds to approximately the midpoint of the CH1 region. It was cloned into a previously constructed full-length mouse IgG1 heavy chain expression plasmid as a SacII/BamHI restriction fragment. All clones were verified by sequencing.

The SEQ ID NOs corresponding to the amino acid sequences of muMAb1 and muMAb2 are shown below in Table 1.

TABLE 1 Full-length heavy and light chain monoclonal antibody sequences mAb Heavy chain mAb Light chain muMAb1 H SEQ ID NO: 2 muMAb1 L SEQ ID NO: 4 muMAb2 H SEQ ID NO: 6 muMAb2 L SEQ ID NO: 8 huMAb1 H SEQ ID NO: 10 huMAb1 L SEQ ID NO: 16 huMAb1 H1 SEQ ID NO: 12 huMAb1 L1 SEQ ID NO: 18 huMAb1 H2 SEQ ID NO: 14 huMAb1 L2 SEQ ID NO: 20 huMAb2 H SEQ ID NO: 22 huMAb2 L SEQ ID NO: 28 huMAb2 H1 SEQ ID NO: 24 huMAb2 L1 SEQ ID NO: 30 huMAb2 H2 SEQ ID NO: 26 huMAb2 L2 SEQ ID NO: 32

Example 6: Humanization

In order to humanize muMAb1 and muMAb2, human immunoglobulin germline sequences having the highest degree of homology to the murine antibody sequences were identified by comparison of the murine sequences to a human immunoglobulin gene database. The results indicated that the closest human germline sequences to the heavy chain of both muMAb1 and muMAb2 was huIGHV4-59x01, and the closest light chain to both muMAb1 and muMAb2 was huIGKV3-11x01.

For humanization of muMAb1 and muMAb2, CDR regions were grafted onto human sequences to create huMAb1 and huMAb2, respectively. The SEQ ID NOs corresponding to the amino acid sequences of huMAb1 and huMAb2 heavy and light chains are shown above in Table 1.

Mutations in the huMAb1 and huMAb2 sequences were designed in silico to maximize degree of humanization and to provide structural support for CDR loops. The amino acid changes and their positions in the heavy and light chain sequences are shown in Tables 2-5 below, as well as in FIGS. 1A, 1B, 2A, and 2B.

TABLE 2 Mutations in huMAb1 heavy chain sequences residue H1 H2 Ile 37 Val Ala 62 Ser Val 67 Leu Val 71 Lys Lys Thr 73 Asn Asn 76 Ser Phe 78 Val Val Arg 97 Lys Lys

TABLE 3 Mutations in huMAb1 light chain sequences residue L1 L2 Ile 2 Asn Asn Leu 47 Trp Ser 65 Arg Thr 69 Asn Phe 71 Tyr Tyr

TABLE 4 Mutations in huMAb2 heavy chain sequences residue H1 H2 Ile 37 Val Ala 62 Ser Val 67 Leu Val 71 Lys Lys Thr 73 Asn Asn 76 Ser Phe 78 Val Val Arg 97 Lys Lys

TABLE 5 Mutations in huMAb2 light chain sequences Residue L1 L2 Ile 2 Asn Asn Leu 47 Trp Thr 69 Asn Asn Phe 71 Tyr Tyr

The SEQ ID NOs. corresponding to the amino acid sequences encoded by the mutated full-length heavy and light chain genes are shown above in Table 1.

The SEQ ID NOs of all CDR sequences of the above antibodies are shown below in Table 6.

TABLE 6 SEQ ID NOs corresponding to CDR regions CDR muMAb1/hMAb1 muMAb2/hMAb2 HCDR1 SEQ ID NO: 33 SEQ ID NO: 40 HCDR2 SEQ ID NO: 34 SEQ ID NO: 34 HCDR3 SEQ ID NO: 35 SEQ ID NO: 41 HCDR2 H1^(a) SEQ ID NO: 39 SEQ ID NO: 39 LCDR1 SEQ ID NO: 36 SEQ ID NO: 42 LCDR2 SEQ ID NO: 37 SEQ ID NO: 43 LCDR3 SEQ ID NO: 38 SEQ ID NO: 44 ^(a)huMAb1 H1 and huMAb2 H1 both include a forward mutation in HCDR2

Example 7: Construction of Humanized Antibody Expression Vectors

Construction of full length humanized heavy and light chain expression plasmids was done using standard recombinant DNA techniques. Fragments were cloned as appropriate into (i) a construct containing full length human IgG1 heavy chain with silent mutations introduced to generate an NheI restriction site at the beginning of the CH1 region, and (ii) a full length human kappa light chain with silent mutations introduced to generate a BsiWI restriction site at the beginning of the CL constant region.

DNA fragments having sequences based on the mutated variants discussed above were synthesized and cloned into the appropriate expression vectors using standard techniques.

Example 8: Production of Recombinant Antibodies Via Transient Transfection in 293T Cells

The human 293T embryonic kidney epithelial cell line was maintained in DMEM (HyClone cat # SH30243.02) supplemented with 10% heat-inactivated fetal bovine serum, 2 mM L-glutamine, and penicillin/streptomycin; (GIBCO cat #15140). Expression constructs were introduced into the cells via poly(ethylenimine) (PEI) mediated transfection. Briefly a DNA mix was prepared by combining heavy and light chain expression plasmids in a 1:1 ratio. PEI/DNA complexes were then formed at a 1.5:1 PEI to DNA ratio, and, after incubation for 20 minutes, added to the cultured cells. Two days after transfection, the culture media were removed and replaced with fresh media. Supernatants were harvested for analysis at day five following the transfection.

Large-scale production of recombinant antibodies was performed by transfecting the heavy and light chain expression plasmids into human 293T cells as described above. After three days, the transfected cells were harvested and seeded into serum free media (HyClone CDM4HEK293 cat # SH3085802) supplemented with 6 mM L-glutamine in shaker flasks. Cell growth and antibody production was monitored and the culture supernatants were harvested for antibody purification when the cell viability fell below 50%.

Expression of different combinations of heavy chains and light chains were performed by co-transfection of heavy and light chain expression plasmids as described above. Affinities of these recombinant antibodies are shown in Table 7 below.

TABLE 7 Summary of binding affinities of recombinant antibodies Anti-SSEA4 Ab Heavy chain Light chain K_(d) (nM) Index^(a) muMAb1 muMAb1 H muMAb1 L 0.17 0.9 muMAb2 muMAb2 H muMAb2 L 0.19 1.1 huMAb1 huMAb1 H huMAb1 L N.D.^(b) —^(c) huMAb1a huMAb1 H2 huMAb1 L1 4.3  23.9  huMAb1b huMAb1 H2 huMAb1 L2 4.7  26.1  huMAb2 huMAb2 H huMAb2 L N.D.^(b) —^(c) huMAb2a huMAb2 H2 huMAb2 L2 5.7  31.7  huMAb3 huMAb1 H2 huMAb2 L 0.09 0.5 huMAb4 huMAb1 H2 huMAb2 L1 0.10 0.6 huMAb5 huMAb1 H2 huMAb2 L2 0.14 0.8 ^(a)Index was obtained by normalizing the K_(d) with the average K_(d) of muMAb1 and muMAb2 (0.18). ^(b)Binding not detected ^(c)Not determined

Biding affinities of two recombinant humanized antibodies, namely, huMAb3 and huMAb4 were also determined by a surface plasmon resonance assay using standard procedures. The K_(d) value of huMAb3 was between 50 nM and 90 nM. The K_(d) value of huMAb4 was approximately 0.4 μM.

The results showed that huMAb3 had a high affinity for SSEA4 as measured by either ELISA or by surface plasmon resonance.

OTHER EMBODIMENTS

All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.

From the above description, one skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Thus, other embodiments are also within the scope of the following claims. 

What is claimed is:
 1. An isolated monoclonal antibody or antigen-binding fragment thereof comprising a heavy-chain CDR1 (H-CDR1) having the sequence of SEQ ID NO: 33, a heavy-chain CDR2 (H-CDR2) having the sequence of SEQ ID NO: 34, a heavy-chain CDR3 (H-CDR3) having the sequence of SEQ ID NO: 35, a light-chain CDR1 (L-CDR1) having the sequence of SEQ ID NO: 42, a light-chain CDR2 (L-CDR2) having the sequence of SEQ ID NO: 43, and a light-chain CDR3 (L-CDR3) having the sequence of SEQ ID NO: 44, wherein the monoclonal antibody or antigen-binding fragment specifically binds to stage-specific embryonic antigen
 4. 2. An isolated monoclonal antibody comprising a heavy-chain having the sequence of SEQ ID NO: 14 and a light-chain having a sequence selected from the group consisting of SEQ ID NO: 28, SEQ ID NO: 30, and SEQ ID NO: 32, wherein the monoclonal antibody specifically binds to stage-specific embryonic antigen
 4. 3. An isolated monoclonal antibody comprising a heavy-chain having the sequence of SEQ ID NO: 2 and a light-chain having the sequence of SEQ ID NO: 4, wherein the monoclonal antibody specifically binds to stage-specific embryonic antigen
 4. 4. An isolated monoclonal antibody comprising a heavy-chain having the sequence of SEQ ID NO: 6 and a light-chain having the sequence of SEQ ID NO: 8, wherein the monoclonal antibody specifically binds to stage-specific embryonic antigen
 4. 5. A method for treating a tumor, the method comprising identifying a subject having a tumor and administering to the subject an effective amount of the monoclonal antibody of claim 1, wherein cells in the tumor express stage-specific embryonic antigen 4 (“SSEA4”).
 6. A method for treating a tumor, the method comprising identifying a subject having a tumor and administering to the subject an effective amount of the monoclonal antibody of claim 2, wherein cells in the tumor express stage-specific embryonic antigen
 4. 7. The method of claim 6, wherein the light-chain sequence is SEQ ID NO:
 28. 